The present invention relates to a process for producing L-threonine using a microorganism belonging to the genus Escherichia and having a resistance to cysteine or cystine, or their analogue and an ability to produce L-threonine.
L-threonine is an amino acid which is not only useful as a medicament such as an amino acid preparation, but also utilizable as an additive for animal feed.
Heretofore, various processes for producing L-threonine by fermentation have been known; for example, a process using a microorganism belonging to the genus Escherichia and having a sensitivity to borrelidin (Japanese Published Examined Patent Application No. 6752/76), a process using a microorganism belonging to the genus Escherichia which requires diaminopimelic acid and methionine and of which threonine biosynthesis system is resistant to the feedback inhibition of threonine (Japanese Published Examined Patent Application No. 10037/81), a process using a microorganism belonging to the genus Serratia which is deficient in threonine dehydrogenase and resistant to threonine metabolic antagonist (Japanese Published Examined Patent Application No. 48195/77), a process using a microorganism belonging to the genus Corynebacterium and having a resistance to .alpha.-amino-.beta.-hydroxyvaleric acid and S-(2-aminoethyl)-L-cysteine, and a requirement for methionine (Japanese Published Unexamined Patent Application No. 19087/72), a process using a microorganism belonging to the genus Brevibacterium and having a resistance to .alpha.-amino-.beta.-hydroxyvaleric acid and S-(2-aminoethyl)-L-cysteine and a requirement for leucine (Japanese Published Unexamined Patent Application No. 31093/75), a process using a microorganism belonging to the genus Brevibacterium and having a resistance to .alpha.-amino-.beta.-hydroxyvaleric acid and S-(2-aminoethyl)-L-cysteine and a requirement for L-isoleucine and L-lysine (Japanese Published Unexamined Patent Application No. 224684/83), and a process using a microorganism belonging to the genus Escherichia and having a resistance to at least one of rifampicin, lysine, methionine, aspartic acid and homoserine, or a decreased ability to degrade L-threonine (Japanese Published Unexamined Patent Application No. 273487/88).